This invention is generally directed to the field of digital cryptographic devices and is more specifically directed to the architecture and method by which a cipher algorithm is stored in the cryptographic apparatus. This invention also addresses a method for manufacturing encrypted communications equipment in an unsecured environment as a result of the cipher algorithm being loaded into the encryption device after the manufacture of the equipment.
In a typical encryption device, a secret key is utilized in conjunction with a cipher algorithm to encrypt and decrypt messages. The keys may be changed as frequently as desired in order to enhance security.
The cipher algorithm which consists of the steps by which the message is encrypted and decrypted using a particular key is frequently protected in order to maintain high levels of security. If the algorithm is known, it becomes easier to decipher a coded message since only the message and key are then unknowns. Thus it is important that the algorithm itself be protected for maximum security applications.
It is also important that the electronic circuits in which the algorithm resides be designed not to fail in a way which would compromise the message being communicated. Algorithms which are stored in logic hardware are easier to be made to "fail safe" than algorithms stored in software. The manufacture of logic hardware containing the cipher algorithms and equipment containing same is often strictly controlled. The manufacture of communications equipment containing such fixed encryption logic requires substantial additional procedures as compared with communications equipment that does not utilize encryption. This results in the need for strict controls and substantially increases manufacturing costs.